(1) Field of the invention
The present invention relates to a magnetic disk device having read/write heads and a servo head both of which are supported by an actuator so as to face surfaces of magnetic disks. The present invention further relates to a flexible printed circuit board on which circuits to be coupled to the read/write heads and the servo head are formed.
(2) Description of the related art
Recently, in computer systems, processing speed and storage capacity have been increased. There is also trend for down sizing thereof. A magnetic disk unit used as an external storage unit of the computer system has been miniaturized, requiring that various components be arranged with a high density in the magnetic disk unit.
In a magnetic disk unit, the actuator drives arms on which magnetic heads are mounted. There are two types of magnetic heads. A first type is referred to as a read/write head used for reading information from and writing information on a magnetic disk. A second type is referred to as a servo head used for reading servo information from a servo surface of a magnetic disk. The actuator is controlled based on the servo information so that the read/write head is positioned on a track of the magnetic disk.
To miniaturize the magnetic disk unit, the actuator must be miniaturized. Due to miniaturization of the actuator, lead wires of the read/write head are close to lead wires of the servo head. An alternating current having a high level flows through the lead wires of the read/write head. Thus, under a condition in which the lead wires of the read/write head are close to the lead wires of the servo head, electro-magnetic waves are generated by the alternating current flowing through the lead wires of the read/write head and noises are thus induced in the lead wires of the servo head by the electro-magnetic waves. The noises induced in the lead wires of the servo head may prevent the servo head from precisely reading out the servo information from the magnetic disk. Thus, it is preferable that the lead wires of the read/write head and the lead wires of the servo head be provided far from each other.
In addition, the read/write head and the servo head are respectively electrically connected to a driving IC and a servo IC. In a read/write operation, large amount of electric current is supplied to the driving IC. Thus, if the driving IC and the servo IC are arranged so as to be close to each other, the electric current supplied to the driving IC affects the servo IC. That is, induced noises occur in the driving IC.
To relieve the above problems, the following circuit arrangement provided between magnetic heads (including read/write heads and a servo head) and ICs has been proposed.
FIG. 1 and FIG. 2 show an actuator for moving a plurality of read/write heads and a servo head. Referring to FIG. 1 and FIG. 2, a plurality of magnetic disks 2 are rotatably supported so as to be provided in layers. The magnetic disks are rotated by a spindle motor (not shown) at a predetermined speed (e.g. 3600 rpm). The enclosure 1 is provided with a magnetic circuit 3 at a corner thereof. The magnetic circuit 3 has a mounting portion 4 to be mounted on the enclosure 1, an inner yoke 5 provided adjacent to the mounting portion 4, and an outer yoke 6 also provided adjacent to the inner yoke 5. A surface of the outer yoke 6 facing the inner yoke 5 is provided with magnets 7 and 8. A surface of the inner yoke 5 facing the outer yoke 6 is provided with magnets 9 and 10. A magnetic gap 11 is formed between a set of magnets 7 and 8 mounted on the inner yoke 5 and a set of magnets 9 and 10 mounted on the outer yoke 6.
An actuator body 15 is rotatably supported by an actuator shaft 12. First and second ends of the actuator shaft 12 are fixed on the mounting portion 4 by screws 13 and 14. The actuator body 15 is provided with a plurality of head arms 16 that extend from a surface thereof toward the magnetic disks 2. The respective head arms 16 are connected to spring arms 17 on which magnetic heads 18 are mounted at ends thereof. The magnetic heads 18 include a servo head for reading out servo information from a surface (referred to as a servo surface) of a predetermined magnetic disk 2' among the plurality of magnetic disks 2 and a plurality of read/write heads for reading out data from and writing data on the surfaces (referred to as data surfaces) of the magnetic disks 2. The magnetic disk 2' having the servo surface is positioned at approximately a middle portion of all the magnetic disks 2. In a case where tracking control of all the magnetic heads 18 with respect to the magnetic disks 2 is performed based on the servo information read out from the magnetic disk 2' positioned at the middle portion of all the magnetic disks 2, the amount of off-tracking of each of the magnetic heads 18 caused by the temperature variation is very small. This tracking servo method is often referred to as a center servo method.
A coil 19 is mounted on the surface of the actuator body 15 so as to be opposite to the head arms 16. The coil 19 is positioned in the magnetic gap 11. When an electric current is supplied from a controller (not shown) to the coil 19, a driving force is generated by an interaction between a magnetic field generated by the coil 19 and a magnetic field in the magnetic gap 11. The actuator body 15 is pivoted on the actuator shaft 12 by the driving force. The amount of pivoting of the actuator body 15 is controlled in accordance with the servo information read out from the servo head, so that the respective magnetic heads 18 are positioned on required tracks of the magnetic disks 2.
A circuit arrangement between the magnetic heads 18 and electric components (e.g. a driving IC and a servo IC) is formed as follows.
A flexible printed circuit board (hereinafter referred to as a FPC board) 32 is used for forming the circuit connecting the magnetic heads 18 to the driving ICs. The FPC board 32 is formed as shown in FIG. 3. Referring to FIG. 1-FIG. 3, the FPC board 32 extends sideways in the long direction, and has an engaging portion 34, a movable portion 35, a bending portion 36 and a projecting portion 37. The engaging portion 34 is fixed on a bracket 31 by screws 33, bracket 31 being mounted on the base plate la so as to extend from the mounting portion 4 of the magnetic circuit 3 toward the magnetic disks 2. The movable portion 35 is mounted on the side surface of the actuator body 15. The bending portion 36 bends in accordance with the pivoting operation of the actuator body 15 between the side surface of the actuator body 15 and the bracket 31. The projecting portion 37 extends either over or under the head arms 16 to a side surface of the actuator body 15 opposite to the side surface on which the movable portion 35 is mounted. The movable portion 35 is provided with a read/write head land 38 having pads to which lead wires of the read/write heads are to be connected. A servo head land 39 having pads to which lead wires are to be connected and an IC mounting land 40 are formed on an leading end area of the projecting portion 37. Printed lines are formed between the pads of the servo head land 39 and the IC mounting land 40. The servo IC are mounted on the IC mounting land 40 of the projecting portion 37. The engaging portion 34 is provided with an IC mounting land 41. Printed lines are formed between the pads of the read/write head land 38 and the IC mounting land 41. Driving ICs are mounted on the IC mounting land 41 of the movable portion 35. A connecting portion 42 is formed at an end of the FPC board 32 opposite to the movable portion 35 and the projecting portion 37. Pads are formed on the connecting portion 42, and printed lines extending from the IC mounting land 40 of the projecting portion 37 and from the IC mounting land 41 of the engaging portion 34 are connected to the pads of the connecting portion 42. Lead wires from a controller (not shown) are connected to the pads of the connecting portion 42.
In the above circuit arrangement, the engaging portion 34 of the FPC board 32 is fixed on the bracket 31 and the projecting portion 37 of the FPC board 32 extends either over or under the magnetic arms 16 to the side surface of the actuator body 15 opposite to the side surface facing the brackets 31. Thus, the driving ICs for the read/write heads and the servo IC for the servo head are separated far from each other.
In addition, the lead wires of each of the read/write heads extend along a side of a corresponding one of the head arm assemblies (including the head arms 16 and the spring arm 17) to the read/write head land 38 of the FPC board 32, lead wires of the servo head extend along a side of a head arm assembly opposite to the side along which the lead wires of the read/write head extend to the servo head land 39 of the FPC board 32. That is, the lead wires of the read/write heads and the servo head are separated by the head arm assemblies.
According to the above circuit arrangement between the magnetic heads and the ICs, the ICs are provided far from each other and the lead wires of the read/write heads and the lead wires of the servo head are separately extend along both sides of the head arm assemblies. Thus, the noises induced in the lead wires of the servo head can be decreased, and the electric current supplied to the driving ICs for the read/write heads is prevented from adversely affecting the servo IC for the servo head.
However, as the projecting portion 37 of the FPC board 32 must extend either over or under the head arms 16 to the side surface of the actuator body 15 opposite to the side surface on which the movable position 35 of the FPC board 32 is to be mounted, it is difficult to mount the FPC board 32 on the actuator. In addition, in order to separately position the lead wires of the lead/write heads and the servo head at the both sides of the head arm assemblies, the projecting portion 37 having the servo land 39 to be connected to the servo head must be projected from the movable portion 35 having the read/write head land 38 to be connected to the read/write head. Thus, a plurality of FPC boards can not be effectively cut out from a sheet-shaped material. As a result, the production cost of the FPC board 32 is increased.